The object of this proposal is to test the feasibility of constructing a bioreactor to achieve large-scale differentiation of stem cells into specific electrically excitable cell types. These cells could offer an unlimited source of material for reconstruction of diseased or damaged muscle and nerve. The instrumentation and techniques developed in this project could have widespread applicability for all types of tissue engineering applications. The concept will be tested by growing embryonic stem cells on cm-size biodegradable scaffolds in a NASA Rotating Bioreactor. The bioreactor, produced by Synthecon, Inc. mimics microgravity, producing optimal nutrient and oxygen perfusion with extremely low shear forces, facilitating the formation of tissue-like aggregates from individual cells. The bioreactor will be modified to deliver biochemical signals and introduce electrical field stimulation. Stem cells will be cultured in the Rotating Bioreactor and subjected to differentiation stimuli. The presence of excitable cells will be assayed by immunohistochemistry and electrophysiological measurements using optical techniques. This will be the first attempt to introduce electrical field stimulation in vitro as a means to promote differentiation of three- dimensional engineered tissue made of stem cells or any primary excitable cell type. PROPOSED COMMERCIAL APPLICATION: The lack of donated organs for transplantation results in thousands of deaths every year in the US and world-wide. Stem cells, with the ability to differentiate into any cell type, have enormous potential to solve this problem. However, it is necessary to develop the means to efficiently expand and differentiate stem cells into functional tissues. The goal of this research is to adapt the NASA-developed Rotating Bioreactor to deliver biochemical and electrical stimuli to three-dimensional cultures of stem cells in order to induce differentiation into muscle and nerve cells. The ability to expand and differentiate stem cells with this technology could provide a virtually unlimited source of tissue for treatment of disease and injury.